Polyethylene terephthalate (also referred to as “PET”) is a polyester of terephthalic acid and ethylene glycol and can be obtained by the polycondensation of dimethyl terephthalate with ethylene glycol, and also terephthalic acid with ethylene glycol. PET exists both as an amorphous (transparent) and as a semi-crystalline (opaque and white) thermoplastic material. Generally, it has useful chemical resistance to mineral oils, solvents and acids but not to bases. Semi-crystalline PET has good strength, ductility, stiffness and hardness. Amorphous PET has better ductility but less stiffness and hardness. PET is used to make bottles for soft drinks and other household, consumer and industrial products.
Unfortunately, despite recycling efforts, billions of pounds of PET are still dumped into landfills annually all over the world. Other PET that is not reused is incinerated. The substantial amount of PET that is disposed into landfills creates significant waste. The incineration of PET wastes significant resources that could be used more effectively.
Thermoplastic molding compositions based on polybutylene terephthalate (also referred to as “PBT”) and fillers are used in various applications. Although conventional PBT-filler molding compositions are useful to many customers, conventional PBT-filler molding compositions generally cannot be made from recycle sources of PBT due to the lack of availability of PBT recycle streams. PET, unlike PBT, is made in much larger quantities and is partially recovered from consumer wastes. If PET (scrap) materials could be converted to PBT and converted into useful molding compositions, then there would exist a valuable way to meet the unmet need to effectively use underutilized scrap PET in PBT thermoplastic molding compositions.
U.S. Pat. No. 5,451,611 teaches a process for converting waste poly(ethylene terephthalate) to either poly(ethylene-co-butylene terephthalate) or poly(butylene terephthalate) (PBT) by reaction with 1,4-butanediol. In discussing the prior art, U.S. Pat. No. 5,451,611 indicates that in most of the processes it cites, the undesirable byproduct diethylene glycol is formed which contaminates the final product and has to be removed by purification before the recovered products can be reused again. A principal object of U.S. Pat. No. 5,451,611 was to provide a process for converting poly(ethylene terephthalate) waste directly to another high value polymer without breaking down the poly(ethylene terephthalate) to its constituent monomers or oligomers. The patent discloses numerous examples in which a variety of polymers have a diol incorporated at various amounts. Example 11 shows a PBT polymer being formed with a complete replacement of ethylene glycol with 1,4-butanediol.
U.S. Pat. No. 5,266,601 teaches a process for making “PBT” from PET by reacting PET with 1,4-butanediol. A principal object of U.S. Pat. No. 5,266,601 was to produce PBT containing less than 1.0 wt. % units of ethylene glycol from PET scrap. Another principal objective of U.S. Pat. No. 5,266,601 was to develop a process that facilitates the reduction of THF generated in the process as much as possible to the extent that this PBT is economically competitive with PBT obtained from monomers. U.S. Pat. No. 5,266,601 emphasizes the production of PBT having ethylene glycol groups in an amount that is less than 1 wt. %. U.S. Pat. No. 5,266,601 discloses that “[a]ny diethylene glycol units in the starting PET are also eliminated as completely as possible” (Col. 3, ll 37-38). The patent discloses “adding only enough 1,4BD [1,4-butanediol] to the PET as is necessary to yield a mixture that can be processed well at the reaction temperature.” The patent discloses that, depending on the PET used “up to 1.0 mol 1,4-BD per mol PET” can be used. In the instances where compositions contain more than 1 wt. % ethylene glycol, U.S. Pat. No. 5,266,601 presents these compositions in comparative examples. Such compositions are described as having “yellowish” and “slightly yellowish” colors, respectively. It is not clear what standard is used in U.S. Pat. No. 5,266,601 to determine the weight percent reported, as the weight percent can reasonably be defined in as follows: (i) a divalent ethylene radical remaining after removal of hydroxyl groups from ethylene glycol, or (ii) a divalent radical remaining after removal of terminal hydrogen atoms from ethylene glycol. Each moeity has different molecular weight and, as such, each moiety can produce a different value.
Japanese laid-open application 2005-89572 teaches a method for producing polybutylene terephthalate by transesterifying bis(2-hydroxyethyl) terephthalate with 1,4-butanediol in the presence of a transesterification reaction catalyst under the pressure of 1-54 kPa at a final temperature ranging from 200-230° C. and then subjecting the reaction product to polycondensation. In one embodiment, the bis(2-hydroxyethyl) terephthalate is obtained by depolymerizing polyethylene terephthalate with excessive ethylene glycol, and purifying the depolymerized product. The patent teaches that transesterifying bis(2-hydroxyethyl)terephthalate with 1,4-butanediol under reduced pressure imparts favorable results.
Unfortunately, such documents do not meet the long felt need of improved use of PET scrap that is ordinarily incinerated or buried in landfills. U.S. Pat. No. 5,451,611, for instance, does not teach effective processes that enable PET to be able to be broken down into its constituent monomers or oligomers—a feature that is sometimes required by commercial considerations. U.S. Pat. No. 5,451,611 does not provide meaningful guidelines for making compositions functionally similar to PBT containing ethylene glycol in amounts other than trace amounts and which exhibit melting temperatures that are higher than those shown in its examples. Similarly, U.S. Pat. No. 5,266,601 does not provide meaningful details about how to make effective PBT materials with ethylene glycol in amounts more than 1.0 wt. % or with other residues that can be found in some PET scrap. Also, U.S. Pat. No. 5,266,601 does not disclose to relatively more versatile processes that can use excess 1,4-butanediol, relative to the PET scrap used or that do not require that the diethylene glycol be “eliminated as completely as possible.” Known technology relating to utilizing PET as scrap materials for making PBT-like materials, in other words, does not provide meaningful solutions that solve the long felt need of new processes for better utilizing PET scrap that is ordinarily incinerated or buried in landfills.
For the foregoing reasons, there is a need to develop improved processes that utilize PET.
For the foregoing reasons, there is a need to develop new processes for making PBT random copolymers having useful performance properties.
For the foregoing reasons, there is a need to develop new articles from molding compositions that utilize PBT derived from PET and that have useful performance properties.